Track expression dependencies (#2113)

src/mbgl/map/map_impl.cpp

@@ -4,9 +4,42 @@
 #include <mbgl/storage/file_source.hpp>
 #include <mbgl/style/style_impl.hpp>
 #include <mbgl/util/exception.hpp>
+#include <mbgl/util/logging.hpp>
+#include <mbgl/util/traits.hpp>
 
 namespace mbgl {
 
+#if !defined(NDEBUG)
+namespace {
+void logStyleDependencies(EventSeverity severity, Event event, const style::Style& style) {
+    using Dependency = style::expression::Dependency;
+    constexpr auto maskCount = underlying_type(Dependency::MaskCount);
+    std::array<std::size_t, maskCount + 1> counts = {0};
+    const auto layers = style.getLayers();
+    for (const auto& layer : layers) {
+        const auto deps = layer->getDependencies();
+        if (deps == Dependency::None) {
+            counts[0]++;
+        } else {
+            for (size_t i = 0; i < maskCount; ++i) {
+                const auto mask = Dependency{1u << i};
+                if ((deps & mask) == mask) {
+                    counts[i + 1]++;
+                }
+            }
+        }
+    }
+    std::ostringstream ss;
+    ss << "Style '" << style.getName() << "' has " << layers.size() << " layers:\n";
+    ss << "  " << Dependency::None << ": " << counts[0] << "\n";
+    for (size_t i = 0; i < maskCount; ++i) {
+        ss << "  " << Dependency{1u << i} << ": " << counts[i + 1] << "\n";
+    }
+    Log::Record(severity, event, ss.str());
+}
+} // namespace
+#endif
+
 Map::Impl::Impl(RendererFrontend& frontend_,
                 MapObserver& observer_,
                 std::shared_ptr<FileSource> fileSource_,
@@ -84,6 +117,10 @@ void Map::Impl::onStyleLoaded() {
         annotationManager.onStyleLoaded();
     }
     observer.onDidFinishLoadingStyle();
+
+#if !defined(NDEBUG)
+    logStyleDependencies(EventSeverity::Info, Event::Style, *style);
+#endif
 }
 
 void Map::Impl::onStyleError(std::exception_ptr error) {